1. Field of the Invention
The present invention relates to a method for detecting an asperity on a parking zone of a disk.
2. Background Information
Hard disk drives contain a plurality of heads that are coupled to a number of magnetic disks. The heads can read information by sensing the magnetic fields of the disks, and write information by varying the magnetic fields of the disks. Information is typically stored within data sectors that are located on annular tracks of the disks.
The heads are typically attached to an actuator arm and a voice coil motor. The voice coil motor can be energized to move the heads to different tracks of the disks.
Each read/write head has an air bearing surface that cooperates with an airflow generated by the rotating disk to create an air bearing between the head and the disks surface. The air bearing reduces mechanical wear between the head and the adjacent disk surface. It is desirable to design an optimum air bearing that will minimize mechanical wear while maximizing the magnetic coupling between the disk and the head.
Some heads contain a magneto-resistive (MR) material that is used to sense the magnetic field of the disks. The resistance of the magneto-resistive material will vary linearly with variations in the magnetic field. The magneto-resistive material is coupled to a current source. Variations in the magnetic field of the disk will cause a corresponding-change in the magneto-resistive resistance and the voltage sensed across the magneto-resistive element. MR heads typically have a higher bit density than other types of disk drive heads.
The disks may have one or more asperities that make physical contact with the heads. The asperity may be a particle that resides on the disk, or an irregularity in the disk surface. The contact between the asperity and the head may cause a momentary increase in temperature of the magneto-resistive material. The increase in temperature will increase the resistance and corresponding voltage sensed across the magneto-resistive element. There have been developed thermal asperity detection circuits that will detect and compensate for the variation in the read signal caused by contact between the head and an asperity.
During operation of the disk drive the heads are located adjacent to the data fields of the disks. When the disk drive is powered down the heads may be moved to parking zones of the disks. The parking zones are typically areas of the disks that have no data. The disk drive may be subject to shock and/or vibration loads that cause the heads to slap the disks. Head slapping may cause damage to the disks and/or heads. Placing the heads in non-data parking zones of the disks insure that data is not corrupted from a head slapping event.
The surfaces of the disks are typically inspected with a disk certifier before being assembled into a hard disk drive. The disk certifier may include optical elements that are used to detect the surfaces of the disks. The certifiers are used to detect and possibly correct defective disks.
Sometimes an asperity is formed after the disks have been inspected and assembled into a drive. For example, an asperity may be formed in the parking zone of a disk during the assembly process. The asperity may decrease the life and reliability of the disk drive. It would be desirable to detect an asperity in the parking zone of a disk after the disk drive has been assembled to screen for defective products before the drive is shipped to a customer.
One embodiment of the present invention is a hard disk drive which has a controller that can move a head to a parking zone of a disk. The disk drive may include a thermal asperity detection circuit that is coupled to the head and can detect an asperity in the parking zone of the disk.